Plasma display device having a thermal conduction medium

ABSTRACT

A plasma display device includes a plasma display panel. A chassis base is disposed substantially parallel to the plasma display panel, and a thermal conduction medium is interposed between and closely contacting the plasma display panel and the chassis base. The thermal conduction medium is a composite sheet having a thermal conductivity which is greater in a planar direction of the composite sheet than the thermal conductivity in a thickness direction of the composite sheet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of Applicants' patent applicationSer. No. 10/867,740 filed in the U.S. Patent & Trademark Office on 16day of Jun. 2004, now U.S. Pat. No. 7,176,605 and assigned to theassignee of the present invention. All benefits accruing under 35 U.S.C.§120 from the parent application are also hereby claimed.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationfor PLASMA DISPLAY DEVICE earlier filed in the Korean IntellectualProperty Office on 23 day of Jun. 2003 and there duly assigned Ser. No.2003-40718.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a plasma display device and, moreparticularly, to a plasma display device having an assembly forefficiently discharging heat generated by a plasma display panel (PDP)to the exterior of the plasma display device.

2. Related Art

A PDP of a plasma display device displays images thereon using plasmagenerated by gas discharge. The PDP generates much heat during operationas a result of the high-temperature discharge gas. Further, if theamount of discharge is increased in an effort to improve brightness, aneven greater amount of heat is generated in the plasma display device.This heat must be efficiently discharged to the exterior of the deviceto enable good operation of the same.

Therefore, in the conventional plasma display device, the PDP isattached to a chassis base made of a high thermal-conductivity material,and a heat discharge sheet (or a thermal conduction sheet) is interposedbetween the PDP and the chassis base. The heat discharge sheet and thechassis base expel the heat generated by the PDP to the exterior of thedevice. The chassis base is typically manufactured through a die castingprocess or a press process using a metal material, while the heatdischarge sheet is made of an acryl- or silicone-based resin.

Many different configurations have been suggested to improve the heatdischarge efficiency of heat discharge sheets. The following describesone such configuration.

A cushioning material is attached along the circumference of the panel,and then a liquid thermal conduction material is applied to the regionsurrounded by the shock-absorbing material. The thermal conductionmaterial is then hardened. Next, the display panel is attached to thesolid thermal conduction material to thereby realize a plasma displaypanel that promotes heat discharge efficiency. Such a structure isdisclosed in Japanese Laid-Open Patent No. Hei 10-172446.

However, a drawback of this configuration is that the thermal conductionmaterial has an isotropic structure that exhibits the same thermalconduction characteristics in all directions. As a result, it isdifficult to minimize localized temperature differences caused byvariations in image patterns.

Further, a plasma display device is disclosed in Japanese Laid-OpenPatent No. Hei 11-251777 in which a thermal conduction sheet isinterposed between a PDP and a thermal conduction plate (chassis base),while heat pipes, heat discharge pins, and a heat discharge plate aremounted on a rear surface of the thermal conduction plate. The plasmadisplay device realizes a uniform distribution of heat through thisstructure. However, such a structure runs counter to efforts to obtain aslim profile and minimize noise generation.

In cases wherein there are differences in the image pattern, heat may beconcentrated at specific areas and bright image sticking may result.“Bright image sticking” relates to a situation wherein a localized areaon the screen stays momentarily brighter than its surroundings after arelatively bright image has been displayed in this localized area. Anexample of how bright image sticking may be generated is described withreference to FIG. 5. As one can see from FIG. 5, after a full whitepattern was continuously displayed on the screen of a PDP 50 for 20minutes, 3% window pattern A, a white region in which 3% load ratio isprovided, is displayed for 10 minutes. Then, if a full white pattern isagain displayed on the screen, a difference in brightness occurs betweentwo portions corresponding to window pattern A and its surrounding areaB, respectively. The 3% window pattern A refers to a white region inwhich a load ratio of as much as 3% is provided. This is a result of thephosphor illumination operation being affected by temperature. Thedifference in temperature between the 3% window pattern A and thesurrounding area B is particularly large when the bright image stickingstarts, and this temperature difference becomes even larger withincreases in a peak brightness.

The generation of bright image sticking reduces picture quality.Therefore, there is a need for heat discharge sheets that provide for agreater thermal conductivity in the planar direction than in thethickness direction of PDP such that heat therefrom can be spread moreuniformly so as to realize a more uniform heat distribution of the same.

SUMMARY OF THE INVENTION

The present invention has been developed to solve above-mentionedproblems. It is, therefore, an object of the invention to provide aplasma display device including a composite sheet having a largeanisotropic thermal conductivity in which thermal conductivity in aplanar direction is greater than in a thickness direction of a plasmadisplay panel (PDP) of the device.

To attain the above object, according to an exemplary embodiment of thepresent invention, a plasma display device includes a plasma displaypanel and a chassis base mounted substantially parallel to the plasmadisplay panel, with a thermal conduction medium being interposed betweenand closely contacting the plasma display panel and the chassis base.The thermal conduction medium is made of a composite sheet havingthermal conductivity in a planar direction greater than that in athickness direction thereof.

Preferably, the thermal conductivity of the composite sheet in theplanar direction is between 5 and 500 times that in the thicknessdirection thereof, that is, between 10 and 1000 W/mK.

The composite sheet has a multi-layered structure of at least threelayers, and each layer has a thermal conductivity different from that ofan adjacent layer.

In another exemplary embodiment of the present invention, the thermalconduction medium is made of a composite sheet having a multi-layeredstructure of at least three layers wherein a high thermal conductivitylayer made of a material with a high thermal conductivity alternateswith a low thermal conductivity layer made of a material with thermalconductivity less than the high thermal conductivity. The thermaldischarge sheet is structured such that thermal conductivity in theplanar direction is greater than that in the thickness direction of thecomposite sheet.

The high thermal conductivity layer can be made of at least one materialselected from the group consisting of carbon, graphite, carbonnanotubes, copper, aluminum, gold, silver, bronze, iron, and zinc. Thelow thermal conductivity layer can be made of a silicone- or acryl-basedhigh polymer adhesive.

Preferably, at least one of the two outermost layers of the compositesheet is made of a low thermal conductivity layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is an exploded perspective view of a plasma display deviceaccording to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a thermal conduction medium of FIG. 1.

FIG. 3 is a side view of a thermal conduction medium according toanother exemplary embodiment of the present invention.

FIG. 4 is a side view of a thermal conduction medium according to yetanother exemplary embodiment of the present invention.

FIG. 5 is a schematic view used to describe the generation of brightimage sticking as a result of the concentration of heat at a localizedarea.

DETAILED DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 is an exploded perspective view of a plasma display deviceaccording to an exemplary embodiment of the present invention, and FIG.2 is a perspective view of a thermal conduction assembly of FIG. 1.

A plasma display device 10 includes a plasma display panel (PDP) 12 anda chassis base 16. The PDP 12 is mounted on the chassis base 16 with oneof its faces adjacent to a face of the chassis base 16, whereas circuitelements 18 for driving the PDP 12 are mounted on the opposing face ofthe chassis base 16.

The chassis base 16 is substantially parallel to the PDP 12, and athermal conduction medium is interposed therebetween. The thermalconduction medium closely contacts the chassis base 16 and the PDP 12 inorder to discharge and spread heat generated by the PDP 12. A frontcover (not shown) is positioned so as to cover exposed surfaces of thePDP 12, and a rear cover (not shown) is positioned so as to coverexposed surfaces of the chassis base 16. The front cover and the rearcover are then interconnected to complete the plasma display device 10.

The thermal conduction medium is an anisotropic composite sheet 14 thathas thermal conductivity in a planar direction (i.e., any direction inthe y-z plane in FIG. 1) that is greater than that in a direction of thethickness of the composite sheet 14 (i.e., the direction x in FIG. 1which is normal to the y-z plane). Preferably, the thermal conductivityin the planar direction is between 5 and 500 times that in the thicknessdirection of the discharge sheet 14. As a result, the flow of heat inthe thickness direction of the composite sheet 14 is minimized, whileheat spread in the planar direction of the composite sheet 14 isincreased. If the thermal conductivity in the planar direction is lessthan 5 times the thermal conductivity in the direction of the thicknessof the composite sheet 14, the desired anisotropic characteristics arenot realized. If, on the other hand, the thermal conductivity in theplanar direction is greater than 500 times the thermal conductivity inthe direction of the thickness of the composite sheet 14, it becomesnecessary to increase the thickness of the composite sheet 14 as theplanar area of the same is increased. This runs counter to efforts atminimizing the thickness of the plasma display device 10.

Preferably, the thermal conductivity in the planar direction is between10 and 1000 W/mK. If the thermal conductivity in the planar direction isless than 10 W/mK, the thermal spread of the panel is insufficientlyfacilitated. On the other hand, if the thermal conductivity in thedirection of the thickness of the composite sheet 14 exceeds 1000 W/mK,the same problem as described above is encountered, that is, it becomesnecessary to increase the thickness of the composite sheet 14 inaccordance with increases in the planar area of the same. This runscounter to efforts at realizing a slim profile of the plasma displaydevice 10.

The composite sheet 14 having the properties as described above has amulti-layered structure in which a plurality of layers of differentthermal conductivities is combined into a single unit. The compositesheet 14 of the exemplary embodiment of the present invention isrealized by closely contacting 9 layers. The layers are placed adjacentto one another by alternating between a high thermal conductivity layer14 a and a low thermal conductivity layer 14 b. However, the presentinvention is not limited to this configuration, and the composite sheet14 may be formed having such an alternating configuration of 3 layers ormore. Stated differently, the composite sheet 14 may be realized bystacking a few to a few tens of the high thermal conductivity layers 14a with one of the low conductivity layers 14 b interposed between eachpair of the high thermal conductivity layers 14 a.

The high thermal conductivity layers 14 a may be made of one or more ofthe following materials: carbon, graphite, carbon nanotubes (CNTs),copper, aluminum, gold, silver, bronze, iron, or zinc. The low thermalconductivity layers 14 b may be made of a silicone- or acryl-based highpolymer adhesive. That is, as a composite having good thermalconductivity and allowing for a planar structure, the high thermalconductivity layers 14 a may be formed of a carbon-carbon composite, astructure that connects CNTs in a planar direction, or a structure thatconnects graphite in a planar direction. Further, the low thermalconductivity layers 14 b are formed by filling spaces between the highthermal conductivity layers 14 a with an adhesive of a low thermalconductivity to thereby complete the composite sheet 14. By forming thecomposite sheet 14 in this manner, anisotropic thermal conductivitiesare exhibited.

At least one of the outermost layers of the composite sheet 14 may be alow thermal conductivity layer 14 b (see FIG. 2). For the compositesheet 14 of the exemplary embodiment described above, both of theoutermost layers of the composite sheet 14 are the low thermalconductivity layers 14 b.

However, with reference to FIG. 3, in a composite sheet 24 according toanother exemplary embodiment of the present invention, only one of thetwo outermost layers is a lower thermal conductivity layer 24 b, whilethe other outermost layer is a higher thermal conductivity layer 24 a.Since these low thermal conductivity layers 14 b and 24 b are made of anadhesive, the adhesivity of the adjacent PDP 12 and/or chassis base 16with the composite sheets 14 and 24 is increased.

Referring to FIG. 4, in yet another exemplary embodiment of the presentinvention, both of the outermost layers of a composite sheet 34 are highthermal conductivity layers 34 a, while lower thermal conductivitylayers 34 b are limited to use as inner layers. In this case, anadhesive (not shown) is thinly applied to outer surfaces of these highthermal conductivity layers 34 a occupying the outermost layers of thecomposite sheet 34, to thereby improve the adhesivity between thiselement and the PDP 12 as well as the chassis base 16.

In the above exemplary embodiments, the high thermal conductivity layers14 a, 24 a, and 34 a may be made of a single material, or may be made bydifferently combining two or more materials. For example, for thecomposite sheet 14, all of the high thermal conductivity layers 14 a maybe made of the same material or each may be made of a differentmaterial.

A thickness d of the composite sheets 14, 24, and 34 (see FIGS. 2, 3 and4) may be determined by considering desired shock-absorbing qualitiesand thermal conductivity, and depending on the overall size of the PDP12.

EXAMPLE

An aluminum filler was placed in a silicone basic material to produce aconventional isotropic heat discharge sheet having thermal conductivityof 0.8 W/mK (comparative example). Then, the heat discharge sheet wasattached to a PDP. Further, high thermal conductivity layers were madeof graphite and low thermal conductivity layers were made of a highpolymer adhesive to produce a composite sheet having thermalconductivity of 6 W/mK in the direction of the thickness of thecomposite sheet and thermal conductivity of 240 W/mK in the planardirection (exemplary embodiment). The composite sheet of the exemplaryembodiment was then attached to a PDP.

Subsequently, various measurements were taken to compare the comparativeexample with the exemplary embodiment. In particular, there weremeasurements of image sticking time, degree of bright image sticking(eye-detecting image sticking), and panel surface temperature. Theresults of the measurements are shown in Table 1 below.

The patterns 50 and pattern display times appearing in FIG. 5 were used.Following the application of a full white pattern to measure imagesticking, there were measurements of the difference in brightnessbetween window pattern A and area B, the time it takes for thedifference in brightness between window pattern A and area B to reach 7cd/m², and the time it takes for image sticking to visibly disappear(eye-detecting image sticking time). In addition, the maximumtemperature of the panel during the entire testing time was measured.The tests were performed by exchanging only the sheets. In Table 1,Exemplary Embodiment 1 and Exemplary Embodiment 2 are composite sheetsof the same structure.

TABLE 1 Comparative Exemplary Exemplary Measurement Example Embodiment 1Embodiment 2 Initial brightness 22 8 11 difference [cd/m²] (after 30seconds) Image sticking time [sec] 170 60 60 (based on 7 cd/m²)Eye-detecting image 180 70 90 sticking [sec] Panel surface 64 53 54temperature [° C.]

As shown in Table 1, the initial brightness difference, image stickingtime, eye-detecting image sticking, and panel surface temperature areall reduced when the composite sheet of the Exemplary Embodiment is usedin place of the conventional heat discharge sheet is used (ComparativeExample).

In the plasma display device that includes the thermal conductionassembly of the present invention described above, an anisotropiccomposite sheet having thermal conductivity in a planar direction whichis greater than that in a thickness direction of the sheet is interposedbetween the chassis base and the PDP. As a result, the accumulation ofheat on the PDP is prevented such that the temperature of the same ismore uniformly distributed, and the generation of bright image stickingis prevented.

Although embodiments of the present invention have been described indetail hereinabove in connection with certain exemplary embodiments, itshould be understood that the invention is not limited to the disclosedexemplary embodiments but, on the contrary, the disclosure is intendedto cover modifications and/or equivalent arrangements included withinthe spirit and scope of the present invention, as defined in theappended claims.

1. A plasma display device, comprising: a plasma display panel; achassis base disposed substantially parallel to the plasma displaypanel; and a thermal conduction medium interposed between the plasmadisplay panel and the chassis base; wherein the thermal conductionmedium is made of a composite sheet comprising at least one high thermalconductivity layer, made of a material of a high thermal conductivity,alternating with at least one low thermal conductivity layer, made of amaterial of a low thermal conductivity less than the high thermalconductivity; wherein said at least one high thermal conductivity layeris made of at least one material selected from a group consisting ofcarbon, carbon nanotubes, copper, aluminum, gold, silver, bronze, iron,and zinc; wherein said at least one low thermal conductivity layer ismade of an acryl-based high polymer adhesive; and wherein the thermalconductivity of the composite sheet in the planar direction is in arange of 5 times to 500 times the thermal conductivity in the thicknessdirection thereof.
 2. The plasma display device of claim 1, wherein thethermal conductivity of the composite sheet in the planar direction isin a range of 10 W/mK to 1000 W/mK.
 3. The plasma display device ofclaim 1, wherein the composite sheet has a multi-layered structure of atleast three layers, and neighboring layers have different thermalconductivities.
 4. The plasma display device of claim 1, wherein atleast one of two outermost layers of the composite sheet is coated withan adhesive.
 5. A plasma display device, comprising: a plasma displaypanel; a chassis base disposed substantially parallel to the plasmadisplay panel; and a thermal conduction medium interposed between, andclosely contacting, the plasma display panel and the chassis base;wherein the thermal conduction medium is made of a composite sheetcomprising at least one high thermal conductivity layer made of amaterial of a high thermal conductivity, and at least one low thermalconductivity layer made of a material of a low thermal conductivity lessthan the high thermal conductivity; wherein said at least one highthermal conductivity layer is made of at least one material selectedfrom a group consisting of carbon, carbon nanotubes, copper, aluminum,gold, silver, bronze, iron, and zinc; wherein said at least one lowthermal conductivity layer is made of an acryl-based high polymeradhesive; and wherein the thermal conductivity of the composite sheet inthe planar direction is in a range of 5 times to 500 times the thermalconductivity in the thickness direction thereof.
 6. The plasma displaydevice of claim 5, wherein the thermal conductivity of the compositesheet in the planar direction is in a range of 10 W/mK to 1000 W/mK. 7.The plasma display device of claim 5, wherein the composite sheet has amulti-layered structure of at least three layers, and neighboring layershave different thermal conductivities.
 8. The plasma display device ofclaim 5, wherein at least one of two outermost layers of the compositesheet is coated with an adhesive.
 9. A plasma display device,comprising: a plasma display panel; a chassis base disposedsubstantially parallel to the plasma display panel; and a thermalconduction medium interposed between, and closely contacting, the plasmadisplay panel and the chassis base; wherein the thermal conductionmedium is made of a composite sheet comprising at least one high thermalconductivity layer, made of a material of a high thermal conductivity,alternating with at least one low thermal conductivity layer, made of amaterial of a low thermal conductivity less than the high thermalconductivity; wherein said at least one high thermal conductivity layeris made of at least one material selected from a group consisting ofcarbon, carbon nanotubes, copper, aluminum, gold, silver, bronze, iron,and zinc; and wherein the thermal conductivity of the composite sheet inthe planar direction is in a range of 5 times to 500 times the thermalconductivity in the thickness direction thereof.
 10. The plasma displaydevice of claim 9, wherein the thermal conductivity of the compositesheet in the planar direction is in a range of 10 W/mK to 1000 W/mK. 11.The plasma display device of claim 9, wherein the composite sheet has amulti-layered structure of at least three layers, and neighboring layershave different thermal conductivities.
 12. The plasma display device ofclaim 9, wherein at least one of two outermost layers of the compositesheet is coated with an adhesive.
 13. A thermal conduction medium madeof a composite sheet, comprising: at least one high thermal conductivitylayer made of a material of a high thermal conductivity; and at leastone low thermal conductivity layer made of a material of a low thermalconductivity less than the high thermal conductivity, said at least onelow thermal conductivity layer alternating with said at least one highthermal conductivity layer; wherein said at least one high thermalconductivity layer is made of at least one material selected from agroup consisting of carbon, carbon nanotubes, copper, aluminum, gold,silver, bronze, iron, and zinc; wherein said at least one low thermalconductivity layer is made of an acryl-based high polymer adhesive; andwherein a thermal conductivity of the composite sheet in a planardirection of the composite sheet is in a range of 5 times to 500 times athermal conductivity of the composite sheet in a thickness directionthereof.
 14. The thermal conduction medium of claim 13, wherein athermal conductivity of the composite sheet in a planar direction is ina range of 10 W/mK to 1000 W/mK.
 15. The thermal conduction medium ofclaim 13, wherein the composite sheet has a multi-layered structurecomprising at least three layers, and neighboring layers have differentthermal conductivities.
 16. The thermal conduction medium of claim 13,wherein at least one of two outermost layers of the composite sheet iscoated with an adhesive.